The present invention relates to a sheet collating machine, and more particularly, to a printed sheet collating machine.
Such collating machines typically include a plurality of feed stations that are located in a row, a collecting conveyor that comprises a collecting channel and an endless conveying chain with pusher dogs which push the printed sheets on the collecting channel, supporting tables which are located between the feed stations and the collecting channel, from which the pusher doges sweep the individually separated printed sheets and transport them onwards, and a device for pre-accelerating the printed sheets before they are acquired by the pusher dogs.
In older-type collating machines, the printed sheets, once separated one from another in the individual feed stations and deposited onto the supporting tables, are accelerated from rest by the pusher dogs that are associated with the collecting conveyor, up to the transport speed of this conveyor. It is well known that this acceleration process is accompanied by a shock which causes distortion and buckling of the printed sheets, and gives rise to malfunctions once a certain speed is exceeded.
These problems occur when operating at high repetition rates, and to counter them, use is made of pre-accelerating devices to bring the printed sheets, once deposited on the supporting tables, up to an initial speed before they are acquired by the pusher dogs.
A known pre-accelerating device is described in published West German Patent Application DE-AS No. 14 86 744. With this device, the supporting tables are caused to reciprocate, all together, in the conveying direction. The printed sheets do not need to be accelerated from rest before being acquired by the pusher dogs of the conveyor, but instead need to be accelerated only from the forward speed of the supporting tables, up to the transport speed of the conveyor.
This pre-accelerating device requires comparatively elaborate constructional arrangements for generating the movement of the supporting tables and, moreover, it cannot be utilized for increasing output still further owing to the fact that heavy masses must be caused to reciprocate.
Furthermore, West German Patent Application DE-AS No. 29 37 611 discloses a device for accelerating printed sheets, wherein use is made of an accelerating means that is rotated by a drive, this accelerating means acting against the supporting table, acquiring the printed sheet lying thereon, and accelerating it in the conveying direction by frictional adhesion.
West German Patent Application DE-OS No. 31 26 808 discloses an arrangement wherein the accelerating means is of bar-shaped design and is set parallel to the supporting table. This design is adapted to prevent comparatively wide printed sheets from twisting, during the accelerating phase, at the moment that they are acquired by the pusher dogs.
The known accelerating devices briefly discussed above involve relatively elaborate and expensive constructional arrangements, and they cannot be utilized for all collating systems because of their bulkiness. Moreover, these accelerating devices require significant set-up time and readjustment to suit the thickness of the printed sheet is also rather time consuming. In addition, it is impossible to exclude the risk of marking the printed sheet while the accelerating means is exerting pressure on the supporting table.